Organic electroluminescent elements (hereinafter, also referred to as “organic EL elements”) utilizing electroluminescence of organic materials have drawn attention as display elements used for thin display devices. Organic EL elements emit light when holes injected from the anode and electrons injected from the cathode recombine within a light-emitting layer disposed between these electrodes. Such organic EL elements spontaneously emitting light have advantages such as high-luminance light emission, a high response speed, a wide viewing angle, a thin profile, and a light weight, and are therefore expected to be applied to various fields such as display panels and illumination lamps.
Organic EL display panels including an organic EL element are usually designed such that the bottom electrode disposed on the substrate is an anode and the top electrode is a cathode. In order to give higher functionality to organic EL display panels having such a structure, an inverted structure in which the bottom electrode is a cathode and the top electrode is an anode have been studied. The following shows the examples thereof.
Patent Literature 1 discloses an organic EL element including, between a light-emitting unit disposed on a bottom electrode and a top electrode, a connection layer that supplies a charge to the light-emitting unit, and a charge transport layer that has charge transporting properties of a reverse conducting type against a charge to be injected from the top electrode, in the order from the light-emitting unit side.
Patent Literature 2 discloses an organic electroluminescent display device having the inverted structure as described above in which an electron-accepting layer having specific properties is disposed between a hole-transporting layer and an anode and an electron-accepting layer having specific properties is disposed between an electron-transporting layer and a cathode.
Patent Literature 3 discloses a light-emitting device including a conductive film made of an inorganic compound with specific properties, between a cathode and an organic compound layer in contact with an anode.
Patent Literature 4 discloses a light-emitting device including a mixture layer containing molybdenum oxide and an aromatic amine compound, disposed in contact with the bottom electrode.